title: Connexin36 contributes to INS-1E cells survival through modulation of cytokine-induced oxidative stress, ER stress and AMPK activity.
abstract: Cell-to-cell communication mediated by gap junctions made of Connexin36 (Cx36) contributes to pancreatic β-cell function. We have recently demonstrated that Cx36 also supports β-cell survival by a still unclear mechanism. Using specific Cx36 siRNAs or adenoviral vectors, we now show that Cx36 downregulation promotes apoptosis in INS-1E cells exposed to the pro-inflammatory cytokines (IL-1β, TNF-α and IFN-γ) involved at the onset of type 1 diabetes, whereas Cx36 overexpression protects against this effect. Cx36 overexpression also protects INS-1E cells against endoplasmic reticulum (ER) stress-mediated apoptosis, and alleviates the cytokine-induced production of reactive oxygen species, the depletion of the ER Ca(2+) stores, the CHOP overexpression and the degradation of the anti-apoptotic protein Bcl-2 and Mcl-1. We further show that cytokines activate the AMP-dependent protein kinase (AMPK) in a NO-dependent and ER-stress-dependent manner and that AMPK inhibits Cx36 expression. Altogether, the data suggest that Cx36 is involved in Ca(2+) homeostasis within the ER and that Cx36 expression is downregulated following ER stress and subsequent AMPK activation. As a result, cytokine-induced Cx36 downregulation elicits a positive feedback loop that amplifies ER stress and AMPK activation, leading to further Cx36 downregulation. The data reveal that Cx36 plays a central role in the oxidative stress and ER stress induced by cytokines and the subsequent regulation of AMPK activity, which in turn controls Cx36 expression and mitochondria-dependent apoptosis of insulin-producing cells.
authors.affiliation: Department of Medicine, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne. Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Allagnat
authors.forename: P
authors.initials: P
authors.lastname: Klee
authors.forename: A K
authors.initials: AK
authors.lastname: Cardozo
authors.forename: P
authors.initials: P
authors.lastname: Meda
authors.forename: J-A
authors.initials: JA
authors.lastname: Haefliger
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D017630:Connexins / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D016207:Cytokines / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D025461:Feedback, Physiological / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000096:biosynthesis; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D053583:Interleukin-1beta / Q000494:pharmacology; D008687:Metformin / Q000494:pharmacology; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D018384:Oxidative Stress / Q000187:drug effects*; D051381:Rats; D026361:Reactive Nitrogen Species / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D000097004:Gap Junction delta-2 Protein
chemical_list: D055372:AMP-Activated Protein Kinases; D002118:Calcium; D053148:Caspase 3; D017630:Connexins; D000242:Cyclic AMP; D016207:Cytokines; D007328:Insulin; D053583:Interleukin-1beta; D008687:Metformin; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species; D000097004:Gap Junction delta-2 Protein